This invention relates to rotary engines in general, and more particularly it is concerned with a Wankel rotary engine of the type which is cooled by an air-fuel mixture intake.
In one type of Wankel rotary engines of the prior art, the suction port is in the form of a side port, while in another type it is in the form of a peripheral port. Generally, the use of a side port as the suction port results in stability of performance of the engines at low speeds because it is possible to avoid overlapping of the suction port and the exhaust port, but has the disadvantage of being unable to obtain high power at high engine speeds because of the facts that the side port cannot be left open for a prolonged time interval and the area of its opening cannot be increased. Meanwhile, when the suction port is in the form of a peripheral port, it overlaps the exhaust port at low speeds and makes the engine performance unstable, but offers the advantage of enabling to obtaining high power at high speeds.
In engines of the type cooled by an air-fuel mixture, the rotor is cooled by an air-fuel mixture intake. In this type of engines, the rotor is heated at high engine speeds and the air-fuel mixture intake is heated by the rotor, thereby resulting in a greatly reduced charging efficiency and making it impossible to obtain high power. To eliminate this disadvantage, the usual practice is to use a bypass port in combination with the side port or the peripheral port, which permits an air-fuel mixture to be supplied direct to the combustion chamber without taking part in the cooling of the rotor.
FIG. 1 shows in sectional view one example of Wankel rotary engines of the type cooled by an air-fuel mixture intake of the prior art. In the figure, side housings are shown at 1 and 2 while a rotor housing is shown at 3. The numeral 4 designates a rotor, the numeral 5 a carburetor, and the numeral 6 a main passage. The numeral 7 refers to a side port, the numeral 8 to a bypass passage, the numeral 9 to a bypass peripheral port, the numeral 10 to a rotor bearing, and the numeral 11 to an eccentric shaft. In another example of Wankel rotary engines of the type described (not shown) of the prior art, the bypass peripheral port 9 is replaced by a bypass side port (not shown) which is formed in the side housing 2 and communicates with the bypass passage 8. The provision of the bypass peripheral port 9 or the bypass side port markedly reduces the resistance offered by the bypass passage 8 to the flow of the air-fuel mixture as compared with the resistance offered by the main passage 6 through the rotor 4. If the size of the bypass port is increased to improve charging efficiency by utilizing the reduction in resistance offered by the bypass passage to the flow of the air-fuel mixture, then the major part of the air-fuel mixture intake passes through the bypass passage 8 and the volume of the air-fuel mixture passing through the main passage 6 decreases. This results in insufficient cooling of the rotor 4, causing seizure between the rotor 4 and the side housings 1, 2 and seizure of the rotor bearing 10. Thus, limits are placed on the size of the bypass port. That is, in the construction shown in FIG. 1, the size of the bypass peripheral port would be restricted with a view to passing the air-fuel mixture through the main passage 6 in an amount sufficiently high to cool the rotor 4, so that the port would have little effect in obtaining high power. Moreover, since the side port 7 is provided in the main passage 6, there is the disadvantage of being unable to obtain high power due to the characteristics of a side port.